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Re: Hey Ari, Alternator Not Working, Please Help Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 5 Oct 2005 05:48:27
In Reply to: Hey Ari, Alternator Not Working, Please Help, ohlins8990, Tue, 4 Oct 2005 20:17:07 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the alternator out of the car, you'll see battery voltage on the green wire. It's just a circuit from the battery, through the key, light, and out to the green wire. Even if it were a bad connection, you'd still see battery voltage, because your meter doesn't pull any current.
2 ohms between the battery terminal and the cable is a lot, but I don't believe your reading. Most consumer DVMs just aren't accurate down that low a resistance. The best test would be to have the battery hooked up, and with an electrical load on (like headlights or parking lights ON), measure the VOLTAGE between the positive battery post and the cable clamp, between the post and alternator post (where the big red wire ends). If you see more than about 50 millivolts (0.05 volts), then there is significant drop in the cable. DO the same with the negative post of the battery to chassis.
Applying a current to the field coil and spinning the alternator is a clever idea. I'm not sure how hard it would be to turn the alternator, as the resistance you would feel (back EMF) would be a function of the speed it spins. You can spin it, but no where as fast as an engine at idle - 1000 rpm is still 16 revolutions a second. At a slow speed it won't have much resistance. I've got to try it some time.
You indicate that the 'alternator isn't giving amps when measured at the battery.' I'm not sure what that means. With the engine off, you should see battery voltage on the battery, about 12.4 volts with a healthy battery, a little lower with a tired battery. When the engine starts, the battery voltage should jump up to around 13 or so. . That shows the alternator is working. You haven't mentioned what the battery voltage is when the engine is running. If you aren't seeing a voltage increase on the battery, but the alternator light goes out, I would strongly suspect a problem with the alternator or battery ground. With the engine running, Measure the voltage between the negative battery post and a good chassis ground. Also CAREFULLY (spinning bits!) measure from the case of the alternator to chassis ground. Chassis, ground, not the engine block. Also measure the engine block to chassis ground. The voltage in all cases should be less than 0.05 volts - very little. There is a ground strap up by the upper motor mount (dogbone) that grounds the engine. Make sure that's OK.
The battery light goes out when the voltage on the field coil increases to around the battery voltage. Usually that happens when the alternator starts working and is not only providing power to the field coils,but the battery, too. However, if the ground is whacked, the ground voltage could be increasing instead, and the battery light goes out.
posted by 192.249....
, Wed, 5 Oct 2005 05:48:27 <-- Viewing This Message
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